Abstract: A method of producing a semiconductor device, comprising the steps of forming a polycrystalline semiconductor layer on the exposed surface of a single crystalline semiconductor substrate, the substrate containing an impurity of one conductivity type and the polycrystalline layer an impurity of the other conductivity type, and heating the polycrystalline layer for the activation thereof at a temperature substantially preventing the impurity contained therein from being diffused into the substrate. The crystal of the substrate is kept free from lattice defect since the impurity is not diffused thereinto. In addition, this method prevents a short circuit from occurring between semiconductor regions of differing conductivity types which would otherwise be caused by deviation in the location of a mask used in the photoetching step.